This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for cooling gas turbine engines.
Gas turbine engines are used as a power source within a variety of applications. To protect the engine from the environment, and to shield a surrounding structure from the gas turbine engine, the gas turbine engine may be mounted within an enclosure that includes an inlet area, an exhaust area, and an engine area that extends between the inlet area and the exhaust area. The enclosure provides a physical structure to contain any engine fires that may ignite, and may include an apparatus to facilitate extinguishing fires within the enclosure. For example, the apparatus may release agents into the enclosure to distinguish the flames, or alternatively, the enclosure may include an apparatus to restrict air from entering the enclosure, thus preventing airflow from fueling the fire.
Because engines generally require continuous airflow for operation, within at least some known modules, the module inlet area includes a duct to route ambient air from outside the module to the engine, and the module exhaust area includes a duct to channel exhaust gases produced during operation of the engine from the module. During operation, heat is constantly generated by the gas turbine engine and various auxiliary equipment. Accordingly, cooling air is also channeled to the interior of the enclosure to facilitate cooling the gas turbine engine and other auxiliary equipment to within reasonable operating parameters. More specifically, at least one known gas turbine engine enclosure includes a fan configured to channel air from a forward end of the enclosure, through the enclosure, and outward through an exhaust duct coupled to an aft end of the enclosure.
However, channeling cooling air axially through the enclosure may generate a non-symmetric cooling airflow with respect to the gas turbine engine. The non-symmetric cooling airflow may cause an upper half of the gas turbine engine casing to receive a greater quantity of cooling air than a lower half of the gas turbine engine casing. Accordingly, non-symmetric thermal gradients may result within the gas turbine engine casing and cause a non-symmetric mechanical distortion of the casing, and eventually blade tips and/or seals may rub against an interior surface of the casing. Specifically, as the blade tip clearance increases, the gas turbine engine performance is reduced and an exhaust an gas temperatures (EGT) margin is reduced.